584 A. W. GRABATJ TYPES OF SEDIMENTARY OVERLAP 



post-Saint Peter time, the great Saint Peter hiatus separating it from the 

 basal sandstone of Cambric age. 



Western Adirondacks and Canada. — Along the western flanks of the 

 Adirondacks the Lowville (upper Chazy) overlaps the preceding forma- 

 tions and rests with a basal sandstone upon the crystallines. This sand- 

 stone grades upward through a calciferous sandrock into the purer lime- 

 stone. The calciferous member has been compared with the Calciferous 

 or Beekmantown of the Mohawk and Champlain valleys, with which it 

 agrees in lithic character; but it is evidently a much higher member of 

 the Ordovicic series. This basal bed is traceable northward to the 

 Frontenac axis, on the west side of which, as at Kingston, Ontario, it is 

 a well marked basal sandstone — the Eideau. This sandstone was for- 

 merly regarded by Canadian geologists as Potsdam, and the overlying 

 formation has been referred to the "Calciferous" (Beekmantown), with 

 which it agrees in lithic character. The occurrence in these overlying 

 beds of Black Eiver fossils, however, proved this correlation to be 

 erroneous, and Ami suggests that the basal sandstone bed may be the 

 shore equivalent of the Chazy. Wilson,* on the other hand, thinks it is 

 the basal arenaceous member of the lower Black River; and this is prob- 

 ably more nearly in accord with the facts. 



In this section and elsewhere in Canada the Trenton limestones (Black 

 River) have been found to rest in places directly upon the crystallines 

 without intervention of basal beds. This fact, as in the case of Sulphur 

 island, is probably to be explained by assuming a slowly submerged island 

 or reef of small extent, from which, in the deepening sea, the siliceous 

 elastics would be removed by the agitated waters. 



On the whole, it may be confidently asserted that it is extremely im- 

 probable that Potsdam or other Upper Cambric formations occur in 

 Ontario west of the Frontenac axis or east of the Sault Sainte Marie, and 

 that the basal sandstone in all this region is therefore of later age, prob- 

 ably in most cases of late Chazy or early Trenton. 



East of the Thousand islands the Potsdam sandstone of New York has 

 been traced northward to the Ottawa, and then eastward past Montreal, 

 along the Saint Lawrence. In some localities along this line the fossil- 

 iferous limestones of the Beekmantown overlap the basal sandstone and 

 rest directly upon the crystallines. In typical exposures the Potsdam 

 grades up into the Beekmantown or Calciferous, the fossils of which are 

 types found near the middle of the Beekmantown of the Champlain valley. 

 At Prescott and Maitland nearly 80 feet of limestones, shales, and sand- 

 stones overlie the Potsdam, and the lower portion of this series carries 



* A. W. G. Wilson : Canadian Record of Sciences, vol. ix, 1903, p. 132. 



